Metal casting from gelatin reliefs



ATES

ALEXANDER MURRAY,

CUM?

"nr mes -R9CHESTER, HEX V YORK, ASSIGIIOR TO EASTM'AIT KODAK Y, O? Bil -3 ESTER, NEE? YORK, A CGRFOR;

'll'QN OF NEW YORK R METAL CASTING FBGM GELATIN BELIEFS No Drawing.

This invention relates to the making of metal casts from gelatin reliefs for the product-ion of photomechanical printing plates.

It is especially useful in metal casting from gelatin molds in which there is comparatively deep detail of microscopic dimensions, such as the screen elements in photomechanical half-tone printing plate matrices.

It is particularly adapt-ed to casting from gelatin molds produced by the method described in the co-pending application, Serial No. 496,341, filed November 17, 1930 by M. Martinez. By that process, gelatin reliefs are developed by heat. ll hen making metal cast-s from such gelatin reliefs, the casting temperature cannot be much in excess of 200 C. and would preferably be about 150 C. (.ltherwise the texture of the surface of the gelatin is ruined and the resulting cast is very poor or practically useless.

ln casting from such molds which contain finc detail, such. fine half-tone dots, considerable difficult v is experienced. As it covers the mold, the metal appears to trap a bubble of air in the depression. This bubble expands with the heat, producing a crater'in the casting instead of a projecting point. The use of graphite and other powders, greases, oils and other cushioning films is of no value. The same is true of lacquers, shellac, asphaltum resins, etc.

lVhile soldering fluxes are common knowledge which contain organic acids such as rosin (abietic acid), oleic acid, lactic acid and organic solvents such as lard oil, tallow, glycerin, etc., such fluxes are .of no value as anti-gas trapping compounds in the method of casting under consideration. The problems in the cases Where fluxes are of value and in the present process do not appear to be analogous even though the removal of metal oxides may be a mutually essential step.

I have found that satisfactory casts may be obtained from gelatin molds such as that described by Martinez if the surface of the mold is coated before casting With a very thin layer of certain organic liquids. It is suflicient to rub the surface with a liquid of the type described, removing any excess of liq- Application filed May 11, 1932. SeriaLNo. 610,745.

uid by fairly vigorous means. If the temperature of the casting-metal is not too high, a

quite sharp cast can then be obtained.

The following formula is a typical and satisfactory example of aloW melting point alloy in parts byfweight Antimony 1.34; Lead 28.58 Tin 16. 52 1 Bismuth 56.56

Melting point approximately 100 C.

After development of therelief, as for example, by the Martinez process, the surface of the relief is treated or coated Withcertain non-aqueous liquids which appear to have a specific tendency to prevent the trapping of as in the de ressions. It is )ossible that this {'3 i 1 il is brought about at least partially by. the

tendency of these substances to dissolve the oxides of the alloy metals. As the metal flows onto the matrix, it probably accumulates avery thin film of oxides on its outer surfaces. This thin film or skin of oxide may then act to prevent the smooth flow of the casting metal into a very small, sharp depression.

In general, these liquids are organic liquids containing no water, they have a boiling point above the temperature of casting and they dissolve the oxides of the alloy metal. In certain cases, they appear to act more satisfactorily if they contain an aromatic ca boxylic acid. Typical liquids Which are especially useful are lso-amyl phthalate Anisaldehyde (linnamaldehyde substance, a small piece of cotton is moistened with iso-amyl phthalate and the surface of the mold is thoroughly wiped with it. Any

, excess of the liquid is carefully rubbed oil another piece of cotton. The mold is then ready for casting which may be done in a. special frame under pressure. While if desired a number of casts may be made without re-treating the surface, it is best if other casts a re to be made to rub the surface of the mold each time with the iso-amyl phthalate.

with

rubbing the surface etccss removed by thoroughly wiping); with absorbent material so that only a lHlllUiL, qua! remains on neimrfacc. Casts can now be made with fusible alloys at. say 150 C. and the metal will'properly fill detail of any ch; 'acter met with on a half-tone screen n atrix.

Emample [ll 7 The followin solution is used Grams n-hutyl phthalate 9O Salicylic acid l "lhis solution wets the surface of the relief without prior treatment. It is preferably applied after development of the relief ust before casting. All excess is wiped away from the surface.

Ewcivnple [V Grams Quinoline Cinnamic acid 2 Benzene 80 This solution can be applied more freely because it is diluted with benzene. When the benzene has evaporated, the remaining ma terial can be wiped down as before.

Example V Grams Iso-propyl lactate l 9o Phthalic acid 5 This liquid again may be used by merely applying, as described, and thoroughly wiping off any excess.

I consider as included in my invention all moiilifications and equivalents coming within the scope of the-a mended claims.

What I claim is:

1. In the process of making a cast with an easily fusible alloy from a gelatin mold in which there fine detail, the step which comprises coating the said mold before casting with a Very thin layer containing an organic liquid selected from the group consisting of iso-amyl-phthalate, n-butyl phthalate, plinoline, is'o-propyl lactate, anisaldehyde, cinnanialdehyde. and decahydronaphthalene.

2. In the process of making a cast with an easily fusible alloy from agelatin mold in which there is fine detail, the step which compri coating the said mold before casting with a wry thin layer containing an aro matic carhmozlic acid and. an organic liquid selected from the group consisting; of isoainyl-phthalate, n-butyl phthalatc, qninoline, i so-propyl lactate, anisaldehyde, cinnamaldehyde and decaliydronaphthalene.

3. In the process of making a. cast with an eafly fusible alloy from a gelatin mold in which there is fine detail, the step which comprises coating the said mold before casting with a very thin layer containing iso-amylhthalate. i

In the process of making a castwith an easily fusible alloyfrom a. gelatin mold in which there is fine detail,the step which comprises coating the said moldbefore casting with very thin layer containing anisaldehyde.

5. In the process of making a cast with an easily fusible alloy from a gelatin mold in which there is fine detail, thestep which comprises coating the said mold before casting with a yery thin layer containing anisic acid and a-nisaldehyde. 7

6. In the process of making; a cast with an easily fusible alloy from a gelatin. mold in which there is fine detail, the step which comprises coating the said mold before casting with a very thin layer containing an aroinatic carboxylic acid and n-butyl phthalato.

Signed at Rochester, -llercYorll', this 5th day of May 1932. a i

ALEXANDER RRAYL 

